Wellbores are typically drilled using a drill string with a drill bit secured to its lower free end and then completed by positioning a casing string within the wellbore and cementing the casing string in position. In recent years, technology has been developed which allows an operator to drill what may be alternately referred to as either a primary or parent wellbore, and subsequently drill what may be alternately referred to as either a secondary or lateral wellbore that extends from the parent wellbore at a desired orientation and to a chosen depth. The parent wellbore is first drilled and then may be at least partially lined with a string of casing. The casing is subsequently cemented into the wellbore by circulating a cement slurry into the annular regions between the casing and the surrounding formation wall. The combination of cement and casing strengthens the parent wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons to an above ground location at the earth's surface where hydrocarbon production equipment is located. In many instances, the parent wellbore is completed at a first depth, and is produced for a given period. Production may be obtained from various zones by perforating the casing string.
At a later time, or while the parent wellbore is being drilled and completed, it is often desirable to drill a lateral wellbore from the parent wellbore. To accomplish this, a casing exit or “window” must be created in the casing of the parent wellbore. The window can be formed by positioning a whipstock in the casing string at a desired location in the parent wellbore. The whipstock is used to deflect one or more mills laterally (or in an alternative orientation) relative to the casing string and thereby penetrate part of the casing to form the window. A drill bit can be subsequently inserted through the window in order to drill the lateral wellbore to the desired length, and the lateral wellbore can then be completed as desired.